One thing to keep in mind on processing speed is that you CAN improve it with practice. My son got a 99% on just about every part on the WISC except PSI which was 40%.
For the last year, we have been doing flashcards and occasional timed math tests. (For some reason, thank goodness, his class isn't doing timed math tests but I'm sure they will come back). I think he's maybe in the top 1/3 now on the timed math tests- OK, not great, but ALOT better.
You can improve these skills by practice.